1. Field of the Invention
The invention relates to a process for neutralizing a layer of acidic water over a sediment in a lake, a pond or a water course comprising a humic substance.
2. Discussion of the Background
Acidification of water in lakes and watercourses is detrimental to aquatic life, because it modifies the biotope fundamentally. It is frequently the result of human activity such as acid rain and certain acidic aqueous residues, but it can also have a natural source, such as waters infiltrating through acidic soils.
A usual means of restoring the biotope of acidic lakes or watercourses consists of neutralizing the acidity of the water by means of a basic reactant such as sodium hydroxide or sodium carbonate, which is scattered onto the surface of the water (OPD--The Chemical Market Newspaper--Apr. 5, 1971--pages 5 and 41: "Soda Ash Helps Sweeten Up the Susquehanna River"). A disadvantageous peculiarity of this known process is that its action is of short duration and that, as a result, it must be frequently repeated.
To overcome this disadvantage, it has also been proposed to exploit the property possessed by the humic substances present in lake sediments, of behaving like cation exchangers by fixing the protons. To this end, consideration has been given to injecting an aqueous solution of sodium carbonate periodically in situ into the sediment, with the aim of regenerating the cation exchanger (Hydrobiologia--vol. 92 (1982)--Dr. W. Junk Publishers (The Hague)--G. K. Lindmark: "Acidified Lakes: sediment treatment with sodium carbonate--a remedy?"--pages 537 to 547). However, this known process involves a complicated and costly apparatus and its implementation is difficult, or even impossible, in the case of the treatment of deep lakes. Furthermore, its action is slow, because the neutralization of protons is effective only on contact with the humic substance in the sediment.